The current invention is generally related to digital watermarks, and more particularly related to pixel-based digital watermarks located near or substantially along edges of an image to be encoded.
In general, it is easy to duplicate digital image data. In recent years, with the proliferation of the internet along with the growing network infrastructure, image databases such as in electronic libraries and other web sites are also readily available to the public. Once digital images are available to a network user, it is difficult to enforce copyrights to prevent the images from being copied. In fact, because the images are digitized, the image duplication is generally unlimited and distributed for potential more duplication. Although there is some law in Japan to prohibit the duplication of certain images such as stock certificates and bank note, it is practically impossible to deter the duplication of images.
In order to solve the above described problems, digital watermarks have been considered. In general, there are two ways to implement digital watermarks. One earlier group of prior art attempts has implemented digital watermarks based upon pixel modifications of images. Although this approach is relatively straight forward, digital watermarks encoded in this manner are susceptible to image processing such as enlargement, reduction and rotation and images are not later correctly decoded. Because of these short comings, prior art has taught away from the use of pixel modification in encoding digital watermarks. The other later group of prior art attempts has involved the use of frequency in an image in encoding digital watermarks. For example, Japanese Patent Laid Publication Hei 9-191394 has disclosed the use of Fourier transformation in encoding information to represent digital watermarks in images. However, since Fourier transformation is calculation-intensive, the processing time is too long for practical use. In addition, if a part of the image is deleted from the encoded image, it is not possible to decode the encoded image. This is because images are generally not uniform in frequency characteristics, and in particular, parts of the image have different low frequency characteristics.
It is desired to improve a method of and a system for encoding a digital watermark in an image and decoding the digital water mark so as to make the digital watermark more resistant to image processing and or image deletion without an inordinate amount of calculation.
In order to solve the above and other problems, according to a first aspect of the current invention, a method of placing a digital watermark in an image, includes the acts of: determining a set of predetermined contiguous pixel patterns of a particular size and at least another set of corresponding predetermined modified contiguous pixel patterns; inputting an input image containing an image and image edges along the image; detecting one of the predetermined contiguous pixel patterns in each of the pixel blocks in the input image; and modifying the input image substantially along the image edges of the input image so as to encode the digital watermark based upon the detected one of the predetermined contiguous pixel patterns and the corresponding predetermined modified contiguous pixel patterns.
According to a second aspect of the current invention, a system for placing a digital watermark in an image, includes: a pixel pattern storage unit for storing a set of predetermined contiguous pixel patterns of a particular size and at least another set of corresponding predetermined modified contiguous pixel patterns; an input unit for inputting an input image, the input image containing an image and image edges along the image; and an encoder unit connected to the pixel pattern storage unit for detecting one of the predetermined contiguous pixel patterns in the input image and for modifying the input image substantially along the image edges of the input image so as to encode the digital watermark based upon the detected one of the predetermined contiguous pixel patterns and the corresponding predetermined modified contiguous pixel patterns according to the encode information.
These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention.